"WITHDRAWN FROM THE ACTION OF GRAVITY. 601 



directly from the free portion of this same superficial layer. The 

 facts which we have related show clearly what is the seat of this 

 second part of the whole configurative action; but they do not 

 make us acquainted with the natui*e of the forces of which it 

 consists. On referring to theory, we find that these forces 

 consist in pressures exerted upon the mass by all the elements 

 of the superficial layer, pressures the intensity of which depend 

 upon the curvatures of the surface at the points to which they 

 coiTespond. Hence it follows that the mass is pressed upon by 

 every part of its superficial layer, with an intensity depending in 

 the same manner upon the curvatures of the surface. For instance, 

 a mass the free surface of which presents a convex spherical curva- 

 ture, will be pressed upon by the whole of the superficial layer be- 

 longing to this free surface, with a greater intensity than if this 

 surface had been plane ; and this intensity will be more con- 

 siderable in proportion as the curvature is greater, or as the radius 

 of the sphere to which the surface belongs is less. Let us see 

 whether experiment will lead us to the same conclusions. 



17. The solid system which we shall employ is a circular per- 

 forated plate (fig. G). It is placed vertically, and attached by a 

 point of its circumference to the iron wire which supports it. 

 Let the diameter of the sphere of oil be less than that of the plate, 

 and let the latter be made to penetrate the mass by its edge in 

 a direction which does not pass through the centre of the sphere. 

 At first, as in the experiment at paragraph 14, the oil will form 

 two unequal spherical seginents ; but matters do not remain in 

 this state. The most convex segment is seen to diminish gra- 

 dually in volume, consequently in curvature, whilst the other 

 increases, until they have both become exactly equal. One part 

 of the oil then passes through the aperture in the plate, so as to 

 be transferred from one of the segments towards the other, until 

 the above equality is attained. 



Let us now examine into the consequences deducible from this 

 experiment, judging from the preceding ones, and independently 

 of all theoretical considerations. When the oil has once become ex- 

 tended over both surfaces of the plate, in such a manner that the 

 superficial layer is applied to every part of the margin of the lattei-, 

 the action of the soUd system is completed ; and the movements 

 which subsequently ensue in the liquid mass, to attain the figure 

 of equilibrium, can only then be due to an action emanating from 

 the free part of the superficial layer. It is therefore the latter which 



VOL. v. PART XX. 2 S 



